How npm start runs a server on port 8000

We have a react application and our development machines are both mac and pc. The start command doesn't work for PC so here is how we got around it:

"start": "PORT=3001 react-scripts start",
"start-pc": "set PORT=3001&& react-scripts start",

On my mac:

npm start

On my pc:

 npm run start-pc

To change the port

npm start --port 8000